A Tidally Disrupted Asteroid around the White Dwarf G29-38

Abstract

The infrared excess around the white dwarf G29-38 can be explained by emission from an opaque flat ring of dust with inner radius of 0.14 R_sun and an outer radius of less than 1 R_sun. This ring lies within the Roche region of the white dwarf where an asteroid could have been tidally destroyed, producing a system reminiscent of Saturn's rings. Accretion onto the white dwarf from this circumstellar dust can explain the observed calcium abundance in the atmosphere of G29-38. Either as a bombardment by a series of asteroids of because of one large disruption, the amount of matter accreted onto the white dwarf may have been ~4x10^24 g, comparable to the total mass of asteroids in the solar system, or equivalently, about 1% of the mass in the asteroid belt around the main-sequence star zeta Lep.